1. Field of the Invention
This invention relates to a phase difference detection apparatus and method for detecting the phase difference between two input signals. The present invention relates also to a reproduction apparatus for performing at least reproduction for an optical disk recording medium and a tracking controlling method for such a reproduction apparatus as just mentioned.
2. Description of the Related Art
In the related art, a DPD (Differential Phase Detection) method is widely known as a servo technique of an optical disk recording medium such as a DVD (Digital Versatile Disc), a BD (Blu-ray Disc: registered trademark) and so forth. The DPD method utilizes the fact that a phase difference appears between detection signals from a detector including at least two detection elements when a laser spot is displaced from the center position of a track on an optical disk recording medium.
In particular, according to an existing DPD method, generally such a four-element detector 11 as shown in FIG. 2 is used to detect the phase difference between sum components (A+C, B+D) of detection signals from the [detector element A, detector element C] and the [detector element B, detector element D] which are individually positioned at diagonal positions.
FIGS. 12A and 12B illustrate the relationships between the phase difference between two signals A+C and B+D and the track displacement in such a DPD method as described above.
It is to be noted that FIGS. 12A and 12B illustrate the relationship between the waveform A+C and the waveform B+D and the relationships between the phase relationship between the waveforms and the track displacement where, in the detector, the detector elements A and D and the detector elements B and C are arranged in order in a disk rotation direction (track longitudinal direction) and the detector elements A and B and the detector elements D and C are arranged in order in a tracking controlling direction (track lateral direction) as in the case of the four-element detector 11 shown in FIG. 2.
As shown in FIG. 12A, a state wherein no phase difference exists between the waveforms A+C and B+D is a state wherein no track displacement exists (that is, a just tracking state).
On the other hand, a state wherein a phase difference appears between the waveforms as seen in FIG. 12b is a state wherein some track displacement appears (that is, a state wherein a laser spot is displaced from the track center). For example, where the phase of the waveform A+C advances with respect to that of the waveform B+D as shown in FIG. 12B, the laser spot is displaced to the side on which the detector elements B and C shown in FIG. 2 are formed. Further, though not shown, where the phase of the waveform B+D advances with respect to that of the waveform A+C, the laser spot is displaced to the side on which the detector elements A and D are formed.
FIG. 13 shows an example of a configuration of an existing tracking error signal production section 50 ready for the case wherein such a four-element detector 11 as described above is used.
First, an addition result A+C of the detection signals from the detector elements A and C in the four-element detector 11 shown in FIG. 2 and another addition result B+D of the detection signals from the detector elements B and D are inputted to the tracking error signal production section 50. The tracking error signal production section 50 includes, as a configuration for inputting the addition results A+C and B+D to produce a tracking error signal, equalizers 51a and 51b, zero-cross timing detection sections 52a and 52b, a phase difference comparison section 53, low-pass filters 54a and 54b, and a differential amplifier 55.
As seen in FIG. 13, the addition result A+C is inputted to the equalizer 51a, by which high-frequency components thereof are emphasized. Then, the resulting addition result A+C is supplied to the zero-cross timing detection section 52a to detect the zero-cross timing thereof.
Further, similarly to the addition result A+C, the addition result B+D is inputted to the equalizer 51b, by which high-frequency components thereof are emphasized. Then, the resulting addition result B+D is supplied to the zero-cross timing detection section 52b to detect the zero-cross timing thereof.
The detection signals of the zero-cross timing detected by the zero-cross timing detection sections 52a and 52b are supplied to the phase difference comparison section 53. The phase difference comparison section 53 compares the zero-cross timing A+C supplied from the zero-cross timing detection section 52a and the zero-cross timing B+D supplied from the zero-cross timing detection section 52b with each other. Then, where the zero-cross timing A+C is earlier than the zero-cross timing B+D (that is, the phase A+C advances with respect to the phase B+D), a positive (+) pulse is outputted, but, where the zero-cross timing B+D is earlier than the zero-cross timing A+C (that is, the phase B+D advances with respect to the phase A+C), a negative (−) pulse is outputted.
The + pulse and the − pulse from the phase difference comparison section 53 are supplied to the low-pass filters 54a and 54b, respectively, as seen in FIG. 13. The low-pass filters 54a and 54b pass only low-frequency components of the input signals from the phase difference comparison section 53 and output the low-frequency components to the differential amplifier 55. The differential amplifier 55 calculates the difference between the input signals from the low-pass filters 54a and 54b and outputs a result of the calculation as a tracking error signal.
With such a configuration as described above, where the number of + pulses is relatively great in the output from the phase difference comparison section 53 (that is, where the ratio is high wherein the phase A+C advances), a tracking error signal having the + polarity is outputted from the differential amplifier 55. On the other hand, where the number of − pulses is relatively great (that is, where the ratio is high wherein the phase B+D advances), a tracking error signal having the − polarity is outputted from the differential amplifier 55.
In this manner, in the existing DPD method, the zero-cross timings of the signal components (in this instance, [A, C] and [B, D]) formed such that the phase difference appears in response to displacement of the laser spot from the track center are detected to obtain information of the phase difference and then the tracking error signal is produced based on the information of the phase difference.
It is to be noted that a related art is disclosed in Japanese Patent Laid-Open No. 2006-53968